The present invention relates to a copier or similar image forming apparatus of the type forming a desired image on a recording sheet by electrophotographic process devices which are implemented as units.
A conventional image forming apparatus, e.g., a copier has a main charger, developing device, transfer charger cleaning device and other process devices arranged around a rotatable photoconductive element Such process devices are sequentially arranged in a particular order and mounted on the framework or similar structural member of the copier body with consideration given to their intervals. Today, while the process devices of a copier are increasing in number and in size to meet the demand for versatile functions, there is an increasing demand for a miniature copier. These contradictory demands make the internal layout of the copier complicated. A copier needs daily maintenance associated with the operation of the copier, e.g., the supply of fresh toner and the discharge of waste toner. Also, when the copier stops operating due to an error such as a paper jam on a transport path or the contamination or deterioration of some process device, the copier has to be inspected and repaired. Such maintenance, as well as periodic inspection, is usually performed by dividing and opening part of interest of the copier. This kind of implementation, however, is not always feasible when it comes to the maintenance and inspection of the individual process units, although desirable for the removal of a jamming sheet. In light of this, the photoconductive element and various process devices may be integrally supported by a process unit, as disclosed in Japanese Patent Laid-Open Publication No. 140264/1985, for example. The process unit is removably mounted on the copier body, and the photoconductive element and process units are each movable relative to the others.
A problem with the conventional process unit scheme is that the process unit cannot be readily inserted into or pulled out from the copier body since the mounting position within the copier body is fixed. The fixed mounting position brings about another problem that in the event of maintenance or inspection the toner deposited on, for example, the process devices is apt to smear the person's body and cloths and/or the person is apt to touch and damage the photoconductive element by accident. Moreover, even the routine work such as the supply of fresh toner cannot be done without calling for a serviceman with expert knowledge since it involves the disassembly of part of the copier body. In addition, when the copier is left unoperated over a long period of time, the photoconductive element and the process units have their contacting portions deteriorated due to the pressure continuously acting thereon and/or the toner is solidified at the contacting portions. Then, when the copier is started to operate again, a stripe pattern or similar defect appears on reproductions.